Answer:
30
Step-by-step explanation:
You can use place value to align the numbers together so you can subtract correctly. Match the ones, tenths, and hundredths digits together to subtract.
4.23
2.75
then you can subtract correctly without any mistakes in place value
If the series is made up of numbers in an arithmetic progression, you have

where

is the first term and

is the common difference between terms.
Since the last term in the series is

, you have

Solve the system

and you'll find that the first term is

(with

).